Ask HN: How do you design experiments on yourself? (health, energy, learning)

How do you design, track, and measure experiments you decide to do on yourself?

Examples of experiments: - Reduce my workouts from three 1h workouts to two 1.5h workouts. - Start taking magnesium supplements for better sleep. - Try intermittent fasting. - Start writing tests first (TDD).

I wonder whether there is a good resource or your anecdote about how to try the "scientific method" on yourself. It seems that some people are better at applying it than others. I think Tim Ferris has been the main person I would think about in this context.